Monopropellants containing quaternary ammonium compounds



3,l8,fil9 Patented Jan. 39, 1962 3,018,619 MONOPROPELLANTS CONTG QUATER- NARY AP/MQNIUM COMPOUNDS Richard C. Doss and William B. Reynolds, Bartlesville,

Okla, assignors to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed July 17, 1959, Ser. No. 827,976 16 Claims. (Cl. 60-35.4)

This invention relates to monopropellant compositions suitable for use in rocket motors, ram-jets, pulse-jets and the like. In a further aspect, this invention relates to a method of operating such motors.

Rocket motors are operated by burning a mixture of fuel and oxidant in a combustion chamber thereof and causing the resulting gases to be expelled through a nozzle at high velocity. Liquid propellants are preferred over solid propellants where it is necessary to vary thrust during flight. Liquid propellants can be classified as bipropellants and monopropellants, and the latter can be either a single compound or mixtures of compounds. Monopropellant systems are advantageous in that they require only one tank, one pump, one nozzle, one fuel line, one set of controls, etc. Furthermore, no mixing or proportioning system is required.

The principal elements of a rocket motor utilizing a liquid fuel comprise a combustion chamber, exhaust nozzle, an injection system, and propellant control valves. The propellant gases are produced in the combustion chamber at pressures governed by the chemical characteristics of the propellant, its rate of consumption, and the cross-sectional area of the nozzle throat. The gases are ejected into the atmosphere through the nozzle with supersonic velocity. The function of the nozzle is to convert the pressure of the propellant gases into kinetic energy. The reaction of the discharge of the propellent gases constitute the thrust developed by the rocket motor.

The following are objects of this invention.

An object of this invention is to provide new monopropellant composition. A further object of this invention is to provide a method for operating rocket motors. Other aspects, objects and advantages of the invention will be apparent to those skilled in the art in view of this disclosure.

In accordance with the invention there are provided new monopropellant compositions which are suitable for use according to the method of the invention in rocket motors and the like. Broadly speaking, the invention comprises a mixture of a quaternary ammonium compound and a suitable oxidant as a monopropellant composition and the use of said composition as a propellant in a rocket motor or the like.

Thus according to the invention there is provided a monopropellant composition comprising a mixture of (1) an oxidant selected from the group consisting of nitric acid containing at least about 70 weight percent HNO and mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 weight percent HClO and not more than about 30 weight percent Water, and (2) at least one quaternary ammonium coinpound characterized by a formula selected from the group consisting of N N 111 R OHz-CHa R 0 III wherein: each R is selected from the group consisting of alkyl, cycloalkyl, alkenyl, and cycloalkenyl radicals containing from 1 to 8 carbon atoms wherein when more than one carbon atom is present the carbon atom attached to the quaternary nitrogen atom is attached to adjoining carbon atoms by single valence bonds, and said radicals substituted with a substituent selected from the group consisting of nitro, nitrato, and cyano radicals, the total number of said substituents in said R groups being not greater than one-half the total number of carbon atoms in said R groups; R is selected from the group consisting of alkylene radicals containing from 1 to 12 carbon atoms, and alkenylene radicals containing from 4 to 12 carbon atoms wherein the carbon atoms attached to the quaternary nitrogen atom is attached to adjoining carbon atoms by a single valence bond; X is an anion selected from the group consisting of nitrate, perchlorate, monohydrogen phosphate, dihydrogen phosphate, hydrogen sulfate, sulfate, hydroxyl, orthoborate, dihydrogen borate, and tetraborate anions; a and b are each integers of from 1 to 4, and the product of a multiplied by the number of quaternary nitrogen atoms is equal to the product of b multiplied by the valence of said anion X; and wherein the ratio of said quaternary ammonium compound to said oxidant is within the range of 0.75 to 1.25 times that of the stoichiometric amount.

It is to be noted that the compounds used in the practice of the invention are quaternary ammonium compounds as distinguished from acid salts of amines. The two classes of compounds are distinctly dififerent chemically. As used herein and in the claims the term quaternary ammonium compound refers to a compound containing at least one nuclear nitrogen atom having its five so-called valence bonds attached to atoms (or radicals) other than a hydrogen atom. For example, such as four nitrogen to carbon bonds and one nitrogen to nitrate (or other anionic radical) bond. In other words, the available valence bonds of said nuclear nitrogen atom are satisfied by other than a hydrogen radical. For example, consider the two compounds (1) trimethylamine nitrate and (2) tetramethyl ammonium nitrate which have the formulas (CH NHNO and respectively. It will be noted that in the acid salt trimethylamine nitrate one of the valence bonds of the nuclear nitrogen atom is satisfied by a hydrogen atom whereas in the quaternary ammonium compound tetramethyl ammonium nitrate all five valence bonds are satisfied by radicals other than hydrogen.

The two classes of compounds can also be distinguished by their reaction with strong bases. For example, when an acid salt such as trimethylamine nitrate is reacted with sodium hydroxide the amine is liberated along with the formation of sodium nitrate and water; whereas a quaternary ammonium compound such as tetramethyl ammonium nitrate has no hydrogen available for the formation of water and there is obtained the tetramethyl ammonium hydroxide, (CH NOH and sodium nitrate, and no free amine is liberated.

As shown hereinafter the monopropellants of the invention using the above defined quaternary ammonium compounds are markedly more stable than monopropellants using acid salts of amines.

Examples of quaternary ammonium compounds suitable for use in the practice of the invention include, among others, the following:

Tetramethylammonium nitrate Tetramethylammonium perchlorate Tetramethylammonium hydrogen sulfate Tetraethylammonium nitrate Triethylmethylammonium hydrogen sulfate Triethylmethylammonium nitrate Triethylmethylammonium perchlorate Triethylmethylammonium dihydrogenphosphate Diethyldimethylammonium nitrate Ethyltrimethylamrnonium nitrate Diallyldimethylammonium nitrate Tetra-n-propylammonium nitrate Tetra-n-propylammonium dihydrogen phosphate Tetra-n-propylam-monium hydrogen sulfate Di(Z-methylhexyl)dimethylammonium perchlorate Tetra-n butylammonium nitrate Tetra-n-butylammonium perchlorate Trimethylpentylammom'um perchlorate Ethyltripentylammonium perchlorate Dihexyldi-n-propylammonium nitrate Ethyltri-n-octylammonium nitrate Tetra-n-octylammonium nitrate Methylytri-n-octylammonium nitrate Methyltri-ternoctylammonium nitrate N,N,N,N'-tetramethyldiethylenediammonium dinitrate N,N,N,N-tetra-n-butyldiethylenediammonium dinitrate Trimethylcyclohexylarnmonium nitrate Trimethylcyclohexylammonium metaborate Allyltrimethylarnmonium nitrate. Triethyl-Z-rnethallylammonium nitrate 3-hexenyltriethylammonium nitrate Di-3-hexenyldimethylammonium nitrate Ethyldimethyl-2-cyclooctenelyamrnonium nitrate Allyldiethylcyclohexylammonium perchlorate N,N,N,N,N',N-hexamethyl methanediarmnoniurn 1 dinitrate N,N,'N,N',N,N'-hexamethyl methanediammonium diperchlorate N,N,N,N',N,N'-hexaethyl methanediammoniurn 1 diperchlorate t N,N,N,N,N,N-hexamethylethane-1,2-diammonium dinitrate t N,N,N,N,N,N'-hexamethylpropane-l,3-diammonium dinitrate N,N,N,N,N,N'-hexamethylbutane-1,4-diammonium dinitrate N,N,N,N,N,N'-hexamethylbutane-1,4-diammonium diperchlorate N,N,N,N',N,N-hexamethyl-butane-1,4-bis(diammonium hydrogen phosphate) N,N,N,N',N',N-hexamethylbutane-l,4-bis(ammonium hydrogen sulfate) 7 N,N,N,N,N,N-hexa-n-propylbutane-1,4-diammonium dinitrate N,N,N,N',N,N-hexarnethyloctane-l,S-diammonium dinitrate V N,N,N,N',N,Nhexamethyldodecane-1,12-diammonium dinitrate N,N,N,N,N,N'-hexa( Z-nitratoethyl) propanel ,3-

diarnmonium dinitrate N,N,N,N,N,N-h.exa(2-cyanoethyl)hexane-1,6-

diammonium dinitrate N,N,N,N,N,N'-hexa(Z-cyanoethyl)hexane-1,4

diammonium dinitrate N,N,N,N',N,N-hexamethyl 2-butene) 1,4-diammonium dinitrate N,N'-dimethyltriethylene diammonium dinitrate N,N'-dimethyltriethylene diammonium diperchlorate N,N'-diethyltriethylene diarnmonium dinitrate N'-ethyl-N@methyltriethylene diammonium dinitrate N,N-diisopropyltriethylene diammonium dinitrate N,N-dicyclohexyltriethylene diarnmonium dinitrate 4 N,N,N,N',N',N'-hexamethyl(4-dodecene)-l,12-

diammonium dinitrate N,N,N,N,N,N-hexaethyl 2,7-diethyl-4-octene) -l ,7-

diammonium dinitrate Tetramethyl ammonium tetraborate Ethyltrimethyl ammonium orthoborate Triethylmethyl ammonium perborate Tetramethylarnmonium hydroxide Tetraethylammonium hydroxide Tetra-n-propylammonium hydroxide Trimethylpentylammonium hydroxide Methyltri-n-octylammonium hydroxide N,N,N,N,N,N'-hexamethylmethane diammonium hydroxide N,N,N,N',N',N'-hexaethyloctane-l,S-diammonium hydroxide The quaternary ammonium compounds described above are oxygen deficient and consequently the monopropellant fuel compositions of my invention require an oxidant. Nitric acid is the presently preferred oxidant for use in the practice of the invention. Since water tends to retard combustion .of the acid with the fuel, the nitric acid is preferably substantially free of Water. Thus, the presently most preferred oxidant is anhydrous nitric acid. However, other more dilute nitric acids can be used in the practice of the invention. White fuming nitric acids and red'fuming nitric acids of varying concentrations are available commercially, and all are useful in the practice of this invention. White fuming nitric acid usually contains about 90 to 99 weight percent HNOg, from 0 to 2 weight percent N0 and up to about 10 Weight percent Water. Red fuming nitric acid usually contains about 70 to 90 Weight percent HNO from 2 to 25 weight percent N0 and up to about 10 weight percent water. Of course, mixtures of the above described acids can be employed to give an acid having any intermediate composition, and all are useful in the practice of this inven tion. Thus, it has been found that nitric acids of all types containing at least about 70 Weight percent HNO are useful as an oxidant in the practice of the invention.

'In addition, it is within the scope of the invention to use mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 Weight percent HClO As an oxidant in the practice of the invention. Said mixtures preferably do not contain more than about 30 weight per cent water.

The monopropellants used in the present invention will be perferably near stoichiometric mixtures of oxidant and quaternary ammonium compound. The ratio of fuel component to oxidant can be in the range of 0.75 to 1.25 times that of the stoichiometric amount. In the practice of the invention said quaternary compounds are commonly used in amounts of about 17 to about 48 weight percent of the mixture of oxidant and quaternary ammonium compound. A slightly fuel-rich mixture is usually required to give an optimum rocket motor performance. As used herein stoichiometric ratio is that ratio of fuel to oxidant calculated by assuming complete combustion of the nitrogen, hydrogen, and carbon of the fuel to N H 0, and CO respectively.

The normally preferred procedure for preparing the monopropellants of the invention is to admix the quaternary ammonium compound, prepared by any suitable method, with nitric acid or other suitable oxidant in the desiredratio at some time prior to use. It is generally preferred to add the quaternary ammonium compound tothe acid oxidant at temperatures below about 50 C., e.g. 0 to 30 C., with good agitation. The length of storage prior to use will depend upon the storage stability of the particular monopropellant composition being employed as V will be shown hereinafter.

Any material which is hypergolic when mixed with nitric acid can be used. Other materials hypergolic with nitric acid such as N,N,N',N'-tetramethylpropane-1,3-diamine; N,N,N',N'-tetramethylpropene-1,3-diamine; furfuryl alstoichiometric amount of standardized alcoholic potas sium hydroxide solution and the resulting potassium chloride which precipitates (essentially quantitative) is cohol; ethylenediamine; etc., can also be used to ignite 5 filtered. The filtrate is then treated with approximately the two-component monopropellant. These hypergols are a excess of the acid corresponding to the quaternary simultaneously injected into the combustion chamber withammonium salt to be prepared, e.g., nitric acid for nitrates, the two-component monopropellant to ignite the monoperchloric acid for perchlorates, etc. After the acid addipropellant. After the two-component monopropellant is tion is complete, the mixture is evaporated to near dryignited, the flow of hypergol is stopped. A temperature- 10 ness on a steam bath. The mushy residue is then dissensitive element, a time mechanlsm or other means can solved in a minimum amount of isopropyl alcohol and the be used to terminate the flow of the hypergol. The monoquaternary ammonium salt precipitates as a white crystalpropellant compositions of the present invention can also line product upon the addition of ethyl ether. The be ignited by other means such as, for example, by an precipitated quarternary ammonium salt is filtered, washed electric igniter. with more ether and dried in a vacuum desiccator. This The quaternary ammonium compounds used in the procedure has been found reliable and the quarternary practice of the invention can be prepared by any of a ammonium salts so prepared are norm-ally obtained in number of suitable methods well known to those skilled yields of 90-98 Weight percent. in the art. A first method, by which the majority of the A second method comprises treating a trialkylamine compounds tested in Example I were prepared, comprises, with a solution of an alkyl nitrate in ethyl ether and alin general, the addition of a suitable alkyl chloride to a lowing the mixture to stand for several days, after which suitable amine which has been dissolved in a highly polar the solvent is evaporated. Triethylmethylammonium solvent much as nitrobenzene. The choice of the alkyl nitrate was obtained by this procedure in a yield of 5.2 chloride, the amine, and the specific reaction temperature percent of theoretical. and quantities of reactants and solvents will of course 20 Athird method comprises treatingasuitable amine with depend upon the particular compound it is desired to prea suitable alkyl halide and then reacting silver nitrate with pare as will be understood by those skilled in the art. the resulting quaternary ammonium halide to produce Methyl alcohol can be used as a co-solvent to increase the the corresponding quaternary ammonium nitrate. Tetrasolubility of the alkyl chloride in the polar solvent, if methylammonium nitrate and triethylmethylammonium desired. After reaction of said alkyl chloride and said nitrate were prepared by this method. amine, the resulting quaternary ammonium chloride is EXAMPLE I separated and dried under vacuum. Said quaternary ammonium chloride is then dissolved in methyl alcohol and Quaternary afnmofllum compounds P p y 0116 f the exact percent of the chloride salt in solution is deterthe above desclilbed Procedures were adIPIXed Wlth i mined gravimetrically by means of silver chloride preci i- 39 drous nitric acid at room temperature in stoichlometric tation. proportions. Properties of the mixtures are given below The thus obtained standardized alcoholic quaternary in Table I.

Table I PROPERTIES OF ANHYDROUS NITRIC AOID-QUATERNARY AMMONIUM COMPOUND MONOPROPELLANTS Umnixed compound Stoichiometric mixtures with anhydrous nitric acid Calculated performance Corn- Oxidizer Freezing Storage Viscosity, Molec- Melting pound to fuel point of stability, Card gap Density centistokes ular point,0. content of ratio solution, hrs. to value gin/ml. Max. O/Fn weight mixture Wa/Ws F. 100 p.s.i. (cards) 2 at 20C. I,

(weight at 200 F. F. 32 F. -40F. percent) Tetramethylammonium 136.2 290 32.9 2. 04 -24 340 2-4 g1 1.396 2. 42 3. 92 225.2 1.455

nitrate. Tetramethylammonium 174.6 290 42.0 (8-16) satd perchlorate. ln. 1. Triethylmethylammonimn 178.2 290 26.1 2.82 94 838 nitrate. Triethylmethylammonium 215.7 290 31.6 2.17 94 478 perchlorate. Triethylmethylammonium 213.2 100-120 27.3 2.67 94 712 dihydrogen phosphate. Triethylmethylammonium 213.3 177-187 28.2 2. 54 (-94 816 1.412 1.95 3.17 12.29

hydrogen sulfate. Tetraethylammom'um 192.3 290 24.9 3.02 94 750 nitrate. Tetraethylammom'um per- 229.7 290 29.8 2.36 195 chlorate. Tetraethylarnmonium di- 227.3 143 and 242.. 26.1 2. 84 94 72 hydrogen phosphate. Tetraethylarnmonium hy- 227.3 290 26.9 2.72 -94 94 drogen sulfate. Tetra-n-propylamrnonium 248.4 260 (dec.) 22.0 3.55 64 360 nitrate. Tetra-n-propyla.mmonium 285.8 241-244 25.3 2. 95 56 38 perchlorate. Tetra-n-propylammonium 283.4 158-170 23.1 3.34 94 381 dihydrogen phosphate. Tetra-n-propylammonium 283.4 136-144 23.6 3.24 -63 288 1.383 1.29 1. 97. 5.88

hydrogen sulfate. N,N' dimethyltriethylene 35. 6 1. s0 43 912 diammonium dinitrate. N,N-diethy1t1'iethylene di- 31. 7 1. 84 94 72 ammonium dinitrate. N ,N' diisopropyltriethly- 29. 2 2. 38 (-94 3 enet diammonium dini- 13. e. N, N, N, N, N, N hexa- 270.3 233d 33.8 1.96 58 1030 22 st.,12 1.443 5.6 11.01 104.6 224.8 1. 399

methylethane 1,2 diam- 14 gl. monium dinitrate.

See footnotes at end of table.

Table l-Continued Unmixed compound Calculated performance Stoichiometric mixtures with anhydrous nitric acid Molecular weight Melting point, 0.

Compound content of mixture (Weight percent) Oxidizer to fuel ratio Wa/Ws 6 Freezing Storage point 1 of stability,

solution, hrs. to

F; 100 p.s.i.

at 200 F.

Viscosity, Card gap centistokes value (cards) 2 Density gm/ml. at C.

Max.

N, N, N, N, N, N hexamethylethane 1,2 diammoni'um diperehlorate.

N, N, N, N, N, N hexamethylethane 1,2 bis- (ummonium hydrogen sulfate).

N, N, N, N, N, N hexaniethylethane 1,2 bis- (ammonium dihydrogen phosphate).

N,N,N,N tetralnethyldiethylenediammonium dinitrate.

N,N,N,N,N,N-hexamethylpropane-1,2-diammonium dinitrate.

N,N,N,N,N,N-hexamethylpropane-1,2-diammonium diperchlorate.

N,N,N,N,N,N-hexamethylpropane 1,2 blS (ammonium dihydrogen phosphate).

N,N,N,N,N,N-hexamethylpropane l,3-diammonium dinitrate.

N,N,N,N,i I,N-hexamethylpropane-l ,3-dianr monium diperchlorate.

N,N,N,N,N,N-hexamethylpropane 1,3 bis (ammonium dihydrogen phosphate).

N,N,N,N,N,N-hexamethylpropane 1,3 bis (ammonium hydrogen sulfate).

N,N,N, ,N,N-hexamethylbutane-1,3- diam monium dinitrate.

N,N,N,N,N,N-hexamethylbutane-lfi-diarnmonium diperchlorate.

N,N,N,N,N,N-hexamethylbutane-1,3-bis (ammonium dihydrogen phosphate).

,N, N, N, N, N hexamethylbutane 1,3 bis- (amrnonium hydrogen sulfate).

N, N, N, N, N, N hexamethylbutane 1,4 didiarnrnonium dinitrate.

N, N, N, N, N, N hexamethylbutane 1,4 diammonium diperehlorate. N, N, N, N, N hexamethylbutane 1,4 bis- (ammonium hydrogen sulfate).

N, N, N, N,N, N hexamethylbutane 1,4 bis- (ammonium dihydrogen phosphate).

' niethylhexane 1,4 diammonium dinitrate.

N, N, N, N, N, N hexamethylhexane 1,6- diammonium diperchlorate.

N, N, N, N, N, N hexamethylhexane 1,6 bis- (ammonium hydrogen sulfate).

N, N, N, ,N,N hexamethylhexane 1,6 bis- (arnmonium dihydrogen phosphate).

, N, N, N, N, N hexaethylethane 1,2 diammonium dinitrate.

238-243 and 242-246.

354.3 220-225 and 354. 4 187-195 and 368. 5 206-214 and 368. 3 110 and 245.-

396. 4 182 and 245- 2. 78 307 6-7tgl., 20-21 1. 327 1. 3. 39 9. 37 223. 8

1 Temperature at which crystal separation begins. 2 gl.=glass cup; st.=steel cup.

3 Leak developed during sample test. 4 Tested-on 30.6 percent salt sample.

' The 'data given in the above Table I show that the thermal stability of the monopropellants of the invention ranges from 23 hours to more than 1080 hours; The

card gap tests show that the monopropellants are resistant 5 Oxidizer to fuel ratio. a Weight of acid/weight of salt.

a Does not form stoichiometric solution. b Glass at.

-24 F. and many are below -94 F., showing that the mono-propellants are suitable for use under arctic or high altitude conditions. The viscosities show that the monopropellants can be readily pumped at temperatures at least to detonation by shock. Freezing points are all below as low as --40 F.

9 EXAMPLE H The excellent thermal stability of the monopropellant compositions of the invention is further illustrated by comparison with other previously known monopropellants. In the comparison given below in Table II the A compounds represent quaternary ammonium compounds of the invention and the B compounds represent acid salts of amines having analogous substituents. A comparison of the tests on said A and B compounds shows that the quaternary ammonium compounds are surprisingly more stable than the corresponding acid salts of amines. Said tests were run on stoichiometric mixtures of said compounds A and B in anhydrous nitric acid.

Table II Weight Storage Test percent stability, No. Compound comhrs. at pound in 200 F.

mixture 1A- N,N,N,N,N,N-hexamethylbutane-l,4- 38. 2 165 diammonium perchlorate. 1B N ,N,N N -tetramethylbutane-1,4-diamine 43. 2 29. 2

perchlorate. 2A--.- Triethylrnethylammonium nitrate 26. 1 838 2B Triethylamine nitrate 27. 7 216 3A.... N,N,N,N,N,N hexamethylpropane 1, 32. 818

3-diammonium dinitrate. 3B N ,N,N ',N -tetramethylpropane-1,3-dia- 36. 1 2. mine dinitrate. I 4A---. N,N,N,N,N,N-hexamethylbutane-1,4- 30. 5 742 diarnmonium dinitrate. 4B N,N,N,N tetramethylbutane 1,4 dia- 33. 8 6.8

mine dinitrate. 5A N,N dimethyltriethylene diammonium 35. 6 912 dinitrate. 53-..- Triethylene diamlne dinitrate 42. 1 4. 5

EXAMPLE III The burning rate at 750 p.s.i.g. pressure was determined for a stoichiometric mixture of anhydrous nitric acid with tetramethylammonium nitrate containing 32.9 weight percent of said nitrate. The equipment employed for the determination of said burning rate consisted of an optical bomb which was designed for the burning of solid propellants. The test was performed by placing 2 milliliters of the propellant mixture in an 8 millimeter glass tube and thereafter placing the tube in the bomb. After closing the bomb and pressuring to the desired pressure with nitrogen, the propellant mixture was ignited by means of a short length of Nichrome resistance wire which was immersed in the surface of the propellant liquid. The time required to burn a finite distance was measured, thus the results are expressed directly in inches per second. The burning rate was 0.02 inch per second at ambient temperature (approximately 70 F.).

The procedures used in carrying out the tests in the above examples are outlined below.

The thermal stability tests were carried out at 200 F. on stoichiometric mixtures of the quaternary ammonium compounds in anhydrous nitric acid. The procedure followed can be summarized as follows. A small glass tube, constructed from 4-inch (I.D.) glass pipe which is able to withstand pressure greater than 1000 p.s.i., is filled about two-thirds full (about 6 ml.) with the monopropellant to be tested. This tube is fitted with a safety head containing a rupture disk which will rupture at about 200 p.s.i. pressure. Said small glass bomb is then placed in a constant temperature bath, containing cold water, and is connected to a pressure recorder and to a supply of compressed nitrogen gas. The pressure in said bomb is raised to 110 p.s.i. with nitrogen to check the system for leaks after which the pressure in said bomb is reduced to 20 p.s.i. The temperature in the constant temperature bath, which can be regulated to maintain a temperature of 200 F., is increased and the time at which a temperature of 200 F. is reached is taken as the start of 10 the test. 'The test is terminated when the pressure in said bomb exceeds p.s.i. or when the rupture disk is ruptured (the pressure rise is often rapid after 100 p.s.i. is reached). The storage life of the propellant at 200 F. is recorded as the time necessary for the pressure in said bomb to increase from 20 to 100 p.s.i.

The shock sensitivity of the monopropellants was determined by the American Rocket Societys Recommended Card Gap Test No. 1, Committee on Monopropellant Test Methods, July 12, 1955. Basically said test consists of placing a 40 ml. sample of the monopropellant above a 50 gram tetryl booster charge and determining the number of 0.01 inch thick cellulose acetate disks (cards) which must be inserted between said booster and the monopropellant to prevent detonation of said monopropellant sample. The following minor modifications were made in the procedure.

In some of the tests the apparatus was modified so that the blasting cap can be inserted as the last step before firing. This procedure is felt to be safer and more convenient than connecting the cap into the system in the first step. This change was made by cutting slots in the cardboard coupling and pellet tubes and by cutting a horizontal slot in the cap-support block. This allows the cap to be inserted in a horizontal position next to the tetryl booster after the test sample has been put into the cup. This modification is quite easily made and permits the continued use of original apparatus with the advantage of an additional safety feature.

Instead of using the prescribed steel cup for holding the monopropellant sample, many of the tests were run using a cup made of Pyrex glass pipe; The dimensions of the glass cup corresponded closely with those of the recommended steel cup:

Glass cup Steel cup dimensions, dimensions, I

inches inches Outside dimension 1. 328 1. 315 W'all thickness 0. 164 0.133 Inside dimension 1.000 1.049

ngth 3 3 at temperatures above the freezing point in view of the low values.

It is to be realized that the storage stability test at 200 F. is a severe test and the mere fact that some compounds give mixtures which have a relatively low storage stability at 200 F. does not mean that said compounds are not useful in the practice of the invention because, at lower temperatures, mixtures of said compounds with nitric acid do have higher storage stabilities than those shown in Table I and can be used at lower temperatures in those instances where storage stability is of secondary importance.

The calculated performance (I values of the monopropellants of the invention were calculated using the following formula and assuming frozen combustion gas composition during isentropic expansion of combustion gases in the rocket nozzle.

K is the ratio of specific heats (C /C for the combustion gases at the arithmetic mean (am) temperature of T and T K is the ratio of specific heats of the combustion gases at the logarithmetic mean (lnm) temperature of T and e T.+T. arn 2 T111111: To To lb. mass ft.

lb. force sec.

M is the average molecular weight of combustion gases at combustion chamber conditions Since many possible embodiments may be made of this invention without departing from the scope thereof, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not in a limiting sense.

We claim: 7 t

1. A monopropellant composition consisting essen tially of a mixture of (1) an oxidant selected from the group consisting of nitric acid containing at least about 70 weight percent HNO' and mixtures of said nitric acid with perchloric acid wherein said mixtures contain up to about 50 weight percent H010 and not more than about 30 weight percent water, and (2) at least one quaternary ammonium compound characterized by a formula selected from the group consisting of wherein: each R is selected from the group consisting of alkyl, cycloakyl, alkenyl, and cycloalkenyl radicals containing from 1 to 8 carbon atoms wherein when more than one carbon atom is present the carbon atom attached to the quaternary nitrogen atom is attached to adjoining carbon atoms by single valence bonds, and said radicals substituted with a substituent selected from the group consisting of nitro, nitrato, and cyano radicals, the total number of said substituents in said R groups being not greater than one-half the total number of carbon atoms in said R groups; R is selected from the group consisting of alkylene radicals containing from 1 to 12 carbon atoms, and alkenylene radicals containing from ,4 to 12 carbon atoms wherein the carbon atom attached to the quaternary nitrogen atom is attached to adjoining carbon atoms by single valence bonds; X is an anion selected from the group consisting of nitrate, perchlorate, monohydrogen phosphate, dihydrogen phosphate, hydrogen sulfate, sulfate, hydroxyl, orthoborate, dihydrogen borate, and tetraborate anions; a and b are each integers offrom -1 to 4, and the product of a multiplied by the number of quaternary nitrogen atoms is' equal to the product of b multiplied by the valence of said anion X; and wherein the ratio of said quaternary ammonium compound to said oxidant is within the range of 0.75 to 1.25 times that of the stoichiometric amount.

2. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N-dimethyltriethylenediammonium dinitrate.

3. The'monopropellant of claim 1 wherein said quaternary ammonium compound is N,N'-diethyltriethylenediammonium dinitrate.

4. The monopropellant of claim 1 wherein said quaternary ammonium compound is N-ethyl-N-methyltriethylene diammonium dinitrate.

5. The monopropellant of claim 1 wherein said quaternary ammonium compound is tetramethylammonium nitrate.

6. The monopropellant of claim 1 wherein said quaternary ammonium compound is tetraethylammonium nitrate.

7. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N,N,N',N',N'-hexamethylpropane-l,3-diammonium dinitrate.

8. The monopropellant of claim 1 wherein said quaternary ammonium compound is N,N,N,N',N,N'-hexamethylbutane-l,3-diammonium dinitrate.

9. In the method for development of thrust by the corn-' bustion of a monopropellant in the combustion chamber of a reaction motor, the step comprising injecting into said combustion chamber a mixture of (1) an oxidant selectedv from the group consisting of nitric acid containing at least 70 weight percent HNO and mixtures of said nitric acid with perchloric acid. wherein said mixtures contain up to about 50 weight percent I-IC1O and not more than about 30 weight percent water, and (2) at least one quaternary ammonium compound characterized by a formula selected from the group consisting of wherein: each R is selected from the group consisting of alkyl, cycloalkyl, alkenyl, and cycloalkenyl radicals containing from 1 to 8 carbon atoms wherein when more not greater than one-half the total number of carbon atoms in said R groups; R is selected from the group consisting of alkylene radicals containing from 1 to 12 carbon atoms, and alkenylene radicals containing from 4 to 12 carbon atoms wherein the carbon atoms attached to the quaternary nitrogen atom is attached to adjoining carbon atoms by single valence bonds; X is an anion selected from the group consisting of nitrate, perchlorate, monohydrogen phosphate, dihydrogen phosphate, hydrogen sulfate, sulfate, hydroxyl, orthoborate, dihydrogen borate, and tetraborate anions; a and b are each integers of from 1 to 4, and the product of a multiplied by the number of quaternary nitrogen atoms is equal to the product of b multiplied by the valence of said anion X; and wherein the ratio of said quaternary ammonium compound to said oxidant is within the range of 0.75 to 1.25 times that of the stoichiometric amount.

10. The method of claim 9 where said quaternary ammonium compound is N,N'-dimethyltriethylenediarnmonium dinitrate.

11. The method of claim 9 wherein said quaternary ammonium compound is N,N'-diethyltriethylenediammonium dinitrate.

12. The method of claim 9 wherein said quaternary ammonium com-pound is N-ethyl-N'-methyltriethylenediammonium dinitrate.

13. The method of claim 9 wherein said quaternary ammonium compound is tetramethylammonium nitrate.

14. The method of claim 9 wherein said quaternary ammonium compound is tetraethylammonium nitrate.

15. The method of claim 9 wherein said quaternary ammonium compound is N,N,N,N',N,N-hexamethylpropane-1,3-diammonium dinitrate.

16. The method of claim 9 wherein said quaternary ammonium compound is N,N,N,N',N',N-hexamethylbutane-1,3-diammonium dinitrate.

No references cited. 

9. IN THE METHOD FOR DEVELOPMENT OF THRUST BY THE COMBUSTION OF A MONOPROPELLANT IN THE COMBUSTION CHAMBER OF A REACTION MOTOR, THE STEP COMPRISING INJECTING INTO SAID COMBUSTION CHAMBER A MIXTURE OF (1) AN OXIDANT SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID CONTAINING AT LEAST 70 WEIGHT PERCENT HNO3 AND MIXTURES OF SAID NITRIC ACID WITH PERCHLORIC ACID WHEREIN SAID MIXTURES CONTAIN UP TO ABOUT 50 WEIGHT PERCENT HCIO4 AND NOT MORE THAN ABOUT 30 WEIGHT PERCENT WATER, AND (2) AT LEAST ONE QUATERNARY AMMONIUM COMPOUND CHARACTERIZED BY A FORMULA SELECTED FROM THE GROUP CONSISTING OF 